This application is related to the disclosures of U.S. Pat. No. 8,670,293, entitled “BROADBAND SOUND SOURCE FOR LONG DISTANCE UNDERWATER SOUND PROPAGATION”, U.S. Pat. No. 4,855,964, entitled “VENTED-PIPE PROJECTOR”, and non-patent literature document entitled “High-efficient tunable sound sources for ocean and bottom tomography, 15 years of operating history”, by Andrey K. Morozov et al., OCEANS 2016 MTS/IEEE Monterey, September 2016, the disclosures of which are hereby incorporated by reference herein in their entirety and for all purposes.
A first test of one aspect of a tunable underwater organ-pipe sound source had been successfully conducted on Nov. 9, 2001. The tunable sound source had many useful characteristics including its ability to operate at any depth underwater. In addition, its output was essentially free of unwanted high frequency harmonics. The acoustical driver of the sound source was tuned to match the frequency and phase of a reference frequency-modulated signal. Over time, this tunable underwater organ-pipe formed the basis for a variety of related devices. In some examples, related devices were designed to have a bandwidth of about 200-300 Hz. Some alternative devices were designed to sweep the frequency of their outputs in a linear manner. In some examples, the sweep range was from about 140 Hz to about 205 Hz. In some examples, the sweep range was from about 500 Hz to about 1000 Hz. In some other examples, the sweep range was from about 800 Hz to about 1200 Hz. In some examples, the sound source could sweep the range of frequencies in about one second. In one example, a sound source was configured to sweep a range of output frequencies in a few minutes. In one example, a tunable sound source configured to sweep its output range in a linear fashion over 135 seconds was employed to make ocean acoustic tomography measurements. In another example, a tunable sound source was configured to emit 80 second narrow-band chirps.
In another example, a tunable underwater sound source has been bottom-deployed in a swept frequency array to produce high-resolution seismic imaging of deep underwater geological formations. Such imaging may be obtained by the use of beam-formed and beam-steered seismic signals to produce high-resolution imaging of geological structures.